Eigen values ....again :(

Hi,

Here is the question that I am stuck on

Construct the matrix X that reduces B to diagonal form through the transformation

Confirm that D is diagonal, that the diagonal elements of D are the

eigenvalues of B and that det(B) = det(D).

So

I then get to the point where and therefore my eigen values are and my eigen vectors as and .

The matrix X is made from the eigen values of B. So . I get as being

Now I have to find the cofactor of X and then transpose of the cofactor in order to eventually get the inverse of X.

which I get as

I now have all the components required to find D.

So when I multiply them all together i get

Which is evidently wrong. Can anyone see roughly where i could have gone wrong and then i will post a more detailed process of what i was doing at that stage.

Thanks for reading and any help that come with it